Android滚轮实现LinearSnapHelper

布满荆棘的人生 2023-10-18 09:05 5阅读 0赞

## Android滚轮实现LinearSnapHelper ##

LinearSnapHelper可以帮助Android的RecyclerView实现滚轮效果，所谓滚轮效果，就是在列表内容滚动时候，总是把某一项内容处于屏幕（视野）正中间。  
本例特意把RecyclerView设置成水平方向，更容易观察出滚轮实现的效果。同时把RecyclerView  
的子item故意设置大一些，左右滑动时候的效果如图，可以看出，总是有一个item处于屏幕正中间：

![70][]

![70 1][]

实现代码：

package zhangphil.test;
    
    import android.graphics.Color;
    import android.os.Bundle;
    import android.support.v7.app.AppCompatActivity;
    import android.support.v7.widget.LinearLayoutManager;
    import android.support.v7.widget.LinearSnapHelper;
    import android.support.v7.widget.RecyclerView;
    import android.util.TypedValue;
    import android.view.LayoutInflater;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.LinearLayout;
    import android.widget.TextView;
    
    public class RVActivity extends AppCompatActivity {
        private RecyclerView mRecyclerView;
        private LinearSnapHelper mLinearSnapHelper;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
    
            mRecyclerView = findViewById(R.id.recycler_view);
    
            LinearLayoutManager mLayoutManager = new LinearLayoutManager(this);
            mLayoutManager.setOrientation(LinearLayout.HORIZONTAL);
            mRecyclerView.setLayoutManager(mLayoutManager);
    
            mLinearSnapHelper = new LinearSnapHelper();
            mLinearSnapHelper.attachToRecyclerView(mRecyclerView);
    
            RecyclerView.Adapter mAdapter = new MyAdapter();
            mRecyclerView.setAdapter(mAdapter);
        }
    
        private class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
            public MyAdapter() {
                super();
            }
    
            @Override
            public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
                View view = LayoutInflater.from(getApplicationContext()).inflate(android.R.layout.simple_list_item_2, null);
                ViewHolder holder = new ViewHolder(view);
                return holder;
            }
    
            @Override
            public void onBindViewHolder(ViewHolder viewHolder, int i) {
                viewHolder.text1.setText(String.valueOf(i));
                viewHolder.text2.setText("pos:" + i);
    
                int n = i % 2;
                int color = n == 0 ? Color.DKGRAY : Color.LTGRAY;
    
                viewHolder.itemView.setBackgroundColor(color);
            }
    
            @Override
            public int getItemCount() {
                return 20;
            }
    
            public class ViewHolder extends RecyclerView.ViewHolder {
                public TextView text1;
                public TextView text2;
    
                public ViewHolder(View itemView) {
                    super(itemView);
    
                    text1 = itemView.findViewById(android.R.id.text1);
                    text1.setTextColor(Color.RED);
    
                    text1.setTextSize(TypedValue.COMPLEX_UNIT_DIP, 160);
    
                    text2 = itemView.findViewById(android.R.id.text2);
                    text2.setTextColor(Color.BLUE);
                }
            }
        }
    }

[70]: https://img-blog.csdn.net/20180921163226401?watermark/2/text/aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5ncGhpbA==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70
[70 1]: https://img-blog.csdn.net/20180921163241935?watermark/2/text/aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW5ncGhpbA==/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70